Dynamic sectorization in a spread spectrum communication system

ABSTRACT

A system and method for dynamically varying traffic channel sectorization within a spread spectrum communication system is disclosed herein. In a preferred implementation, the system is operative to convey information to at least one specified user in a spread spectrum communication system and includes a first network for generating, at a predetermined chip rate, a first pseudorandom noise (PN) signal of a first predetermined PN code. The first PN signal is then combined with a first information signal in order to provide a resultant first modulation signal. The system further includes a second network for providing a second modulation signal by delaying the first modulation signal by a predetermined delay inversely related to the PN chip rate. A switching transmission network is disposed to selectively transmit the first and second modulation signals respectively to first and second coverage areas.

This is a continuation of application Ser. No. 08/195,003 filed Feb. 14,1994 now abandoned.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to communication systems utilizing spreadspectrum signals, and, more particularly, to a novel and improved methodand apparatus for dynamic channel sectorization within a spread spectrumcommunication system.

II. Description of the Related Art

Communication systems have been developed to allow transmission ofinformation signals from a source location to a physically distinct userdestination. Both analog and digital methods have been used to transmitsuch information signals over communication channels linking the sourceand user locations. Digital methods tend to afford several advantagesrelative to analog techniques, including, for example, improved immunityto channel noise and interference, increased capacity, and improvedsecurity of communication through the use of encryption.

In transmitting an information signal from a source location over acommunication channel, the information signal is first converted into aform suitable for efficient transmission over the channel. Conversion,or modulation, of the information signal involves varying a parameter ofa carrier wave on the basis of the information signal in such a way thatthe spectrum of the resulting modulated carrier is confined within thechannel bandwidth. At the user location the original message signal isreplicated from a version of the modulated carrier received subsequentto propagation over the channel. Such replication is generally achievedby using an inverse of the modulation process employed by the sourcetransmitter.

Modulation also facilitates multiplexing, i.e., the simultaneoustransmission of several signals over a common channel. Multiplexedcommunication systems will generally include a plurality of remotesubscriber units requiring intermittent service of relatively shortduration rather than continuous access to the communication channel.Systems designed to enable communication over brief periods of time witha set of subscriber units have been termed multiple access communicationsystems.

A particular type of multiple access communication system is known as aspread spectrum system. In spread spectrum systems, the modulationtechnique utilized results in a spreading of the transmitted signal overa wide frequency band within the communication channel. One type ofmultiple access spread spectrum system is a code division multipleaccess (CDMA) modulation system. Other multiple access communicationsystem techniques, such as time division multiple access (TDMA),frequency division multiple access (FDMA) and AM modulation schemes suchas amplitude companded single sideband are known in the art. However,the spread spectrum modulation technique of CDMA has significantadvantages over these modulation techniques for multiple accesscommunication systems. The use of CDMA techniques in a multiple accesscommunication system is disclosed in U.S. Pat. No. 4,901,307, issuedFeb. 13, 1990, entitled “Spread Spectrum Multiple Access CommunicationSystem Using Satellite or Terrestrial Repeaters”, assigned to theassignee of the present invention.

In the above-referenced U.S. Pat. No. 4,901,307, a multiple accesstechnique is disclosed where a large number of mobile system users, eachhaving a transceiver, communicate through satellite repeaters orterrestrial base stations using CDMA spread spectrum communicationsignals. In using CDMA communications, the frequency spectrum can bereused multiple times thus permitting an increase in system usercapacity. The use of CDMA results in a much higher spectral efficiencythan can be achieved using other multiple access techniques.

In particular, cellular CDMA systems communication between a basestation and subscriber units within the surrounding cell region isachieved by spreading each transmitted signal over the available channelbandwidth by using a unique user spreading code. In such CDMA systemsthe code sequences used for spreading the spectrum are constructed fromtwo different types of sequences, each with different properties, toprovide different functions. There is an outer code that is shared byall signals in a cell or sector that is used to discriminate betweenmultipath signals. In addition, adjusting the phase of the outer codeallows it to be used to discriminate between sets of users grouped into“sectors” within a given cell. For example, the users within a givencell may be partitioned into three sectors by providing three phases ofthe outer code. There is also an inner code that is used to discriminatebetween user signals transmitted over a plurality of “traffic channels”associated with each user sector. Specific transmitted signals areextracted from the communication channel by despreading the compositesignal energy in the communication channel with the inner codeassociated with the transmitted signal to be extracted.

Referring to FIG. 1A, there is shown a first exemplary cell 10 in whichare disposed a plurality of subscriber units 12 and a base station 14.As is indicated by FIG. 1A, the cell 10 is partitioned into six coverageareas C1-C6. The base station 14 may include a set of six fixed-beamantennas (not shown) dedicated to facilitating communication withsubscriber units in the coverage areas C1-C6, respectively. Thesubscriber units 12 are grouped into a plurality of user sectors, eachof which supports an equivalent number of traffic channels. As isindicated by FIG. 1A, a first residential user sector encompasses thecoverage areas C1 and C6; while a second residential user sector spansthe coverage area C4. Similarly, a user sector including primarily ruralareas is associated with the coverage areas C2 and C3, while businessusers are concentrated within the coverage area C5.

As is indicated by FIG. 1A, it is necessary that certain user sectors berelatively narrow in order to accommodate demand during peak periods ofsystem utilization. For example, the relatively narrow breadth of thebusiness user sector is necessitated by the high concentration ofbusiness users within coverage area C5 desiring to communicate duringworking hours, e.g., between 8 a.m. and 5 p.m. That is, if the scope ofthe business user sector were expanded to include regions other thancoverage area C5 it is possible that an insufficient number of trafficchannels would be available during business hours to accommodate allthose desiring to place calls. In contrast, the diffuse concentration ofsubscriber units 12 among rural dwellings allows the traffic channelsassociated with the rural user sector to be allocated among usersdistributed over two coverage areas C2-C3.

Unfortunately, during non-working hours a number of the traffic channelsdedicated to the business user sector will likely go unused, since atsuch times there exist significantly fewer business callers and acorrespondingly larger number of residential callers. Accordingly, itwould be desirable to be able to provide a high concentration of trafficchannels to business users within coverage area C5 during businesshours, and to provide a relatively lower traffic channel concentrationduring non-working hours.

Although there exist antenna arrays capable of adaptively shaping aprojected beam in response to changing user demand, implementation ofsuch antenna arrays within the system of FIG. 1A would requirecorresponding modification of the fixed-beam architecture of the basestation 14. In addition, the relatively sophisticated RF/microwavecircuits typically employed in adaptive beam-forming networks result inincreased system cost and complexity. Accordingly, it is an object ofthe invention to provide a cost-effective technique for varying theconcentration of traffic channels in response to changes in thedistribution of users within a spread spectrum cellular communicationsystem.

In the specific instance of a CDMA communication system, each usersector is capable of supporting a given level of traffic demand.Accordingly, it is a further object of the invention to tailor the sizeof specific user sectors within a CDMA communication to the trafficchannel demand within the sector. Such efficient traffic channelallocation would enable optimum utilization of communication systemresources, thereby minimizing the cost per user.

In addition to addressing the need for flexible traffic channelallocation as a consequence of the short-term changes in user demanddescribed above, it is a further object of the invention to accommodatelong-term changes in user demand. Such long-term variation in demandcould arise from, for example, shifts in population distribution andbuilding patterns within a given geographic area.

A further disadvantage of conventional fixed-beam systems, such as thesystem of FIG. 1A, is that relatively accurate estimates of user demandmust typically be available prior to system installation. That is,system designers generally must be supplied with detailed informationrelated to expected demand patterns in order that the fixed-beam basestation be configured to provide the requisite traffic channel capacityto each user sector. Changes in usage patterns occurring proximate theinstallation period thus tend to prevent optimal utilization of theavailable traffic channels. It is therefore yet another object of thepresent invention to provide a communication system capable of beingtailored, upon installation, in accordance with existing patterns oftraffic channel demand.

SUMMARY OF THE INVENTION

The present invention provides a system and method for dynamicallyvarying traffic channel sectorization within a spread spectrumcommunication system.

In a preferred embodiment, the system of the invention is operative toconvey information to at least one specified user in a spread spectrumcommunication system. The system includes a first network forgenerating, at a predetermined chip rate, a first pseudorandom noise(PN) signal of a first predetermined PN code. The first PN signal isthen combined with a first information signal in order to provide aresultant first modulation signal. The system further includes a secondnetwork for providing a second modulation signal by delaying the firstmodulation signal by a predetermined delay inversely related to the PNchip rate. A switching transmission network is disposed to selectivelytransmit the first and second modulation signals respectively to firstand second coverage areas. In this way selective transmission of thefirst and second modulation signals may be used to vary the size of thefirst user sector during different system operating periods. The firstuser sector is associated with a first set of traffic channels, one ofwhich is allocated to the specified user.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and features of the invention will be more readilyapparent from the following detailed description and appended claimswhen taken in conjunction with the drawings, in which:

FIG. 1A shows an exemplary cell, included within a cellularcommunication system, in which is disposed a plurality of subscriberunits and a base station.

FIG. 1B shows a second exemplary cell as sectorized in accordance withthe invention during normal business hours.

FIG. 1C depicts the second exemplary cell as sectorized during eveninghours in accordance with the invention.

FIG. 1D shows a block diagram representation of an exemplary basestation communications transceiver in which the dynamic sectorizationsystem of the invention is embodied.

FIG. 2 provides a block diagrammatic representation of a base stationtransmitter network configured to provide dynamic user sectorization inaccordance with the invention.

FIG. 3 depicts a switch matrix, disposed within the base stationtransmitter, for providing a switchable connection between theinformation signal associated with each user sector and a set of sixantenna drivers.

FIG. 4 depicts a block diagram of a base station transmitter networkcapable of providing increased user sectorization by utilizing bothhorizontally and vertically polarized antenna beams.

FIGS. 5A and 5B respectively provide top and side views of a dual-moderesonant patch antenna incorporated within a preferred implementation ofthe base station antennas.

FIG. 6 shows a block diagrammatic representation of a base stationreceiver network configured to provide dynamic user sectorization inaccordance with the invention.

FIG. 7 provides a block diagrammatic representation of an exemplaryspread spectrum transmitter.

FIG. 8 depicts a pilot generation network for providing I and Q channelpilot sequences.

FIG. 9 shows an exemplary implementation of an RF base stationtransmitter.

FIG. 10 is a block diagram of an exemplary diversity receiver disposedwithin a subscriber unit.

FIG. 11A illustratively represents the azimuth pattern of a 40 degreefixed-beam assumed to be projected by a first base station antennaassociated with one of the coverage areas C1-C6 (FIG. 1A).

FIG. 11B illustratively represents the azimuth pattern produced when anadjacent pair of fixed-beam base station antennas are driven in phase.

FIG. 12 shows a block diagrammatic representation of a base stationtransmitter network configured to provide dynamic user sectorization byprojecting a set of in-phase beams to each user sector.

FIG. 13 depicts an alternate base station configuration for providingdynamic user sectorization by projecting a set of in-phase beams.

FIG. 14 shows a triangular arrangement of first, second and third phasedarray antenna panels collectively operating to provide a set of nineantenna beams.

FIG. 15 depicts a preferred implementation of the antenna panels of FIG.14, each of which includes a 4×4 array of patch elements.

FIG. 16 is a block diagram of a beam-forming network used to drive aphased array antenna panel.

DESCRIPTION OF THE PREFERRED EMBODIMENT

I. Introduction

Turning now to FIG. 1B, there is shown a second exemplary cell 18 assectorized in accordance with the invention during normal businesshours. As is indicated by FIG. 1B, the second cell 18 is sectorized intoa set of nine user sectors U1-U9. The second cell 18 is partitionedduring business hours such that a set of four user sectors U1-U4, eachspanning an angle of, for example, 20 degrees, are allocated to adensely populated business center. During business hours the lesspopulated rural and residential areas of the cell are serviced by a setof relatively broader user sectors U5 and U6-U9, respectively. In anexemplary embodiment the angular width of the rural user sector U5 isset at 100 degrees, the residential user sectors U6, U8 and U9 are eachof 40 degrees, and the residential user sector U7 is of 60 degrees. Thenarrow breadth of the user sectors U1-U4 is necessitated by the highconcentration of users within the business center desiring tocommunicate during working hours. In this way the confined scope of theuser sectors U1-U4 ensures that a sufficient number of traffic channelsare available during working hours to accommodate a desired number ofusers within the business center.

FIG. 1C depicts the second exemplary cell 18 as sectorized duringevening (i.e., non-working) hours into a plurality of nine user sectorsU1′-U9′ in accordance with the invention. As is indicated by FIG. 1C,during non-working hours a single user sector U1′ of 80 degrees, ratherthan the four 20-degree sectors U1-U4 required during working hours, isemployed to service demand within the business center. Similarly, thepopulation shift to residential areas during the evening hours requiresthe increased sectorization provided by the seven user sectors U2′-U6′,and U7′-U9′, relative to the four sectors U6-U9 required during thedaytime. In the exemplary embodiment the angular width of residentialuser sectors U2′-U4′ and U8′-U9′ is set at 20 degrees, and the angularwidth of the residential user sectors U6′ and U7′ is set at 40 degrees.The rural user sector U5′ remains at 100 degrees during both day andevening hours as a consequence of the typically minimal temporalvariation in user demand throughout rural regions. The change insectorization illustrated by FIGS. 1B-1C may be achieved using thedynamic sectorization system of the invention, the operation of which isdescribed below with reference to the block diagram of FIG. 1D.

FIG. 1D shows a block diagram representation of an exemplary basestation communications transceiver 25 in which the dynamic sectorizationsystem of the invention is embodied. As is discussed below, thetransceiver 25 operates to provide improved service to users disposedwithin a first cell of a cellular communications system by dynamicallyvarying the allocation of traffic channels among various user sectorswithin the cell. The transceiver 25 is seen to include a controller 27,an antenna system 29 and transmit/receive channel banks 31. Controller27 is typically programmed to provide channel set-up/assignment of thetransmit/receive channel banks 31. The transmit/receive channel banks 31are electromagnetically coupled to the antenna system 29 via a waveguidetransmission line 32 or the like. Each individual channel bank maycomprise, for example, a plurality of channel units capable offacilitating communication with a particular user. In the embodiment ofFIG. 1D, the transmit/receive channel banks 31 supply beam-formingsignals to the antenna system 29 so as to sectorize the first cell intoa plurality of user sectors, each of which has associated therewith aplurality of user traffic channels. Information signals are relayedbetween the channel banks 31 and an external communications network,e.g., a public switched telephone network (PSTN), over a data bus 33.

In a first preferred embodiment of the invention, a fixed number oftraffic channels are associated with each user sector. Under thisconstraint the present invention contemplates accommodating variationsin user demand within the various regions of the cell by adjusting therelative size of each user sector. For example, a number of relativelynarrow user sectors could be employed to service the users within aparticular area of the cell during periods of high user demand. Thismaximizes the likelihood that a traffic channel will be available to allthose desiring to establish communication during such periods ofheightened demand. Conversely, during periods of minimum demand arelatively fewer number of user sectors of wider width could be utilizedto provide the requisite traffic channel capacity. Such widening of theuser sectors associated with a particular cell area during periods ofreduced demand allows for efficient use of the fixed number of trafficchannels assigned to each user sector. That is, by increasing thegeographic extent of user sectors during periods of minimal demand, thenumber of likely system users included within each user sector can beheld relatively constant. This prevents excess traffic channel capacityfrom developing in user sectors directed to a given geographic area inthe event of decreases in user concentration, i.e., demand, within thegiven area.

It is to be understood, however, that in alternate embodiments of thepresent invention, the number of traffic channels allocated to aparticular user sector may be varied in response to changing demandconditions. In addition, the present invention may enable even furtherimprovement in traffic channel utilization by allowing for alteration ofboth the geographic size of, and the number of traffic channelsassociated with a given user sector.

In a presently preferred embodiment of the invention statistics relatingto channel usage within each user sector are monitored by the associatedones of the channel banks 31 and conveyed to controller 27 by way of afirst control bus 34. Control information from the controller 27respectively received by the channel banks 31 and the antenna system 29over the first control bus 34, and a second control bus 35,respectively, allows traffic channels to be allocated to user sectors onthe basis of the usage statistics supplied by the channel banks 31. Thatis, the beam pattern projected by antenna system 29 is adjusted in orderthat a selected set of traffic channels are provided to each usersector. In the presently preferred embodiment, the monitored channelusage is displayed to an operator (not shown) by controller 27, thusallowing specification of the desired cell sectorization. In anautomated mode, controller 27 is programmed to assign channels and/orsector size based upon channel usage statistics.

In other embodiments of the invention the controller 27 may beconfigured to monitor channel usage by virtue of information receivedfrom the channel banks 31 over the first control bus 34. The pertinentchannel usage information could again be displayed to an operator inorder to enable appropriate adjustment of the size of each user sector.Alternately, the controller 27 could be programmed to automaticallyprovide channel setup/assignment commands to the channel banks 31 on thebasis of the monitored channel usage, again obviating the need forcontrol information to be supplied by an operator.

Although in the presently preferred embodiments of the invention thesize of each user sector is adjusted through alteration of the beampattern projected by the antenna system 29, in other implementations anequivalent modification of sector size could be achieved throughprocessing of the beam-forming signals supplied by the channel banks 31.In such implementations, the beam-forming signals processed by thechannel banks 31 would be weighted and combined prior to being providedto, or received from, the antenna system 29. In this way dynamicsectorization could be achieved by providing control information tosignal processing electronics (not shown) coupled to the channel banks31, rather than by supplying such information to the antenna system 29.

Referring again to FIG. 1D, it would appear that one way ofaccommodating variation in user demand would be to configure the basestation antenna system 29 to provide a plurality of fixed antenna beamsusing an associated set of fixed-beam antenna elements. In such anarrangement each base station antenna would project a beam of fixedwidth over one of a set of adjacent coverage areas. Differing numbers ofthe coverage areas would then be assigned to each user sector on thebasis of expected usage requirements. In this way changes in userconcentration could be addressed by dynamically varying the number offixed antenna beams used to carry the traffic channels associated with agiven sector.

One difficulty presented by such an approach is that significantdistortion in beam pattern could be expected to arise proximate theboundaries between coverage areas included within a given user sector.As was discussed in the Background of the Invention, in certain cellularcommunication systems a long PN code of predetermined phase is used tomodulate the information signals carried by the traffic channels of agiven user sector. If such information signals modulated with the longPN code of the given user sector were then projected by a pair offixed-beam antennas into adjacent coverage areas, an arbitrary phasedifference would exist between the identical PN-modulated signalscarried by each beam. Such phase difference could be engendered by, forexample, variation in the lengths of the signal paths from thebeam-forming network of the base station to each fixed-beam antenna.Since these PN-modulated signals are not aligned in phase at theboundary of the beam coverage area, the resulting coherent interferencewould tend to distort the beam pattern by producing nulls and otherirregularities. The resultant signal fading accompanying such patterndistortion would then degrade the signal-to-noise-ratio of thePN-modulated signal received by any proximately located subscriber unitreceivers.

II. Dynamic Sectorization Using Transmit Antenna Array

As is described hereinafter, in a preferred embodiment the presentinvention contemplates using an arrangement of fixed-beam antennas todynamically vary the area encompassed by each user sector. As employedherein, the term “dynamic user sectorization” is intended to bedescriptive of the process of varying the size of a set of user sectorsbetween successive system operating periods. In accordance with theinvention, a delay is introduced between each pair of identicalPN-modulated signals projected to adjacent coverage areas within a givenuser sector, thereby decorrelating each such pair of signals. In thepreferred embodiment a delay having a duration slightly longer than theperiod of a chip of the PN long code is used to decorrelate the signalsprojected to adjacent coverage areas within each user sector. Asubscriber unit positioned at a coverage area boundary is thus able todiscriminate between, and hence to separately receive, the decorrelatedPN-modulated signals provided to the adjacent coverage areas. Theseparately received signals are then time-aligned within the receiverusing conventional techniques of diversity reception, and are despreadusing a locally-generated replica of the long PN code.

Applying the technique of the invention to the system of FIG. 1A, delayswould be introduced at least between the signals projected to coverageareas C1 and C6 of the first residential user sector, and between thesignal pairs provided to coverage areas C2 and C3 of the rural usersector. Although in a preferred embodiment delays are also introducedbetween the signal pairs projected to adjacent coverage areas withindifferent user sectors (e.g., between the signal pair provided tocoverage areas C3 and C4), such signal pairs are assumed to beindependently decorrelated as a consequence of the differing PN longcode phase associated with each user sector.

Referring to FIG. 2, there is shown a block diagrammatic representationof a base station transmitter network 40 configured to provide dynamicuser sectorization in accordance with the invention. The network 40 isseen to include first, second and third spread spectrum transmitters 42,44, and 46 for processing baseband information signals to be transmittedover traffic channels associated with first (#1), second (#2) and third(#3) user sectors. A PN long code generator 50 provides the long PN codeused by the transmitters 42, 44 and 46 in modulating the informationsignals transmitted to each user sector. The relative phases of the PNlong codes supplied to the transmitters 42, 44 and 46 are offset bypredetermined margins by phase delay elements 52 and 54. In thepreferred embodiment, the phase delay elements 52 and 54 provide delaysapproximately equivalent in duration to 768 PN chips. With thetransmitters 42, 44 and 46 the PN-modulated information signals are usedto bi-phase modulate a quadrature pair of sinusoids. The modulatedsinusoids are then summed, bandpass filtered, shifted to an RF carrierfrequency, and provided to transmit amplifiers 58, 60 and 62. Theamplified signals produced by the amplifiers 58, 60 and 62 comprise thePN-modulated information signals to be provided via an RF carrier touser sectors #1, #2, and #3, respectively. The outputs of each of theamplifiers 58, 60 and 62 are respectively connected to six-way splitternetworks 66, 68 and 70. As is indicated by FIG. 2, the splitter networks66, 68 and 70 are coupled to a switch matrix 74.

As is described in further detail with reference to FIG. 3, the switchmatrix 74 provides a switchable connection between the informationsignal associated with each user sector and a set of six antenna drivers75-80. That is, the switch matrix 74 allows the information signals fromany user sector to be routed to users within any of the coverage areasC1-C6. The antenna drivers 75-80 are associated with a set of six basestation antennas 85-90, each antenna 85-90 being operative to project abeam over one of the coverage areas C1-C6 (FIG. 1A). Each antenna driver75-80 is further seen to include an input summation node 92. Thesummation nodes 92 are each coupled to switch matrix 74 through a set ofthree input signal lines, each signal line carrying the PN-modulatedinformation signals corresponding to either user sector #1, #2 or #3.

As noted above, in a preferred embodiment, delays are introduced betweenthe signals projected to any pair of adjacent coverage areas.Accordingly, the antenna drivers 75-80 are seen to include delayelements 94A-95F capable of providing delays slightly longer than thechip period of the PN code provided by PN long code generator 50. In apreferred embodiment alternate ones of the delay elements 95A-95F (e.g.,elements 95B, 95D, and 95F) are designed to provide a delay slightlylonger than a single PN chip period, while the remaining delay elements(e.g., elements 95A, 95C, and 95E) are omitted (zero delay). The delayelements 95A-95F could be realized using one or more surface acousticwave (SAW) filters. Alternately, a coiled optical fiber of predeterminedlength could be used to create the desired delay. Each antenna driver75-80 also includes a power amplifier 96 for providing an output signalto one of the antennas 85-90.

Referring to FIG. 3, there is shown an illustrative representation ofthat portion of the switch matrix 74 operative to switchably connect thesix-way splitter 66 to each of the antenna drivers 75-80. In particular,digitally-controlled attenuators 97A-97F are interposed between theoutputs of the splitter 66 and the antenna drivers 75-80. If, forexample, it was desired that the first user sector encompass coverageareas C2-C4, then attenuators 97A, 97E and 97F would be set to maximumattenuation, while the attenuators 97B-97D would be turned off (i.e.,set to provide zero attenuation). In a preferred embodiment the switchmatrix 74 includes two other sets of six digital attenuators (notshown), substantially identical to the attenuators 97A-97F, forswitchably connecting the splitters 68 and 70 to the antenna drivers75-80.

The attenuators 97A-97F will preferably have a dynamic range ofapproximately 30 dB, and should be capable of being adjusted in 1 dBincrements. In this way the beam projected to a particular coverage areamay be gradually extinguished, and then gradually established onceagain, during a transition between sector configurations. For example,if it were desired to modify the scope of the first user sector so thatit included only coverage areas C3-C4 rather than C2-C4, attenuator 97Bwould be incrementally adjusted from zero to maximum attenuation.Assuming it were desired to simultaneously increase the scope of thesecond user sector, the setting of an attenuator (not shown) connectedbetween the second antenna driver 76 and the splitter 68 sector wouldcontemporaneously be changed from maximum to zero attenuation. Thedigital attenuators 97A-97F are of a type available from, for example,Anzac Corp., such as Part No. AT-210.

Although in the implementation of FIG. 3, the switch matrix 74 isconfigured to allow any user sector to encompass any combination ofcoverage areas C1-C6, it is understood that in alternate embodiments thematrix 74 could be simplified by limiting the potential scope to threeor four coverage areas.

Referring to FIGS. 1A and 2, each of the antennas 85-90 is designed toproject a 60 degree beam to one of the six coverage areas C1-C6. It isunderstood, however, that increased sectorization could be achieved byutilizing nine antennas, each of which would be designed to project a 40degree beam. In addition, dual-mode antennas capable of providing bothhorizontally and vertically polarized beams could be employed toaccommodate up to twice as many users within each coverage area. As isdescribed below with reference to FIG. 4, separate antenna drivers areused to generate the signals projected by each horizontally andvertically polarized beam.

Referring to FIG. 4, there is shown a block diagram of a base stationtransmitter network 100 disposed to provide increased user sectorizationby employing both horizontally and vertically polarized antenna beams.The network 100 is seen to include first, second and third pairs ofspread spectrum transmitters 102A-102B, 104A-104B, and 106A-106B, forprocessing baseband information signals to be transmitted over first(#1A-1B), second (#2A-2B) and third (#3A-3B) paired sets of trafficchannels associated with a corresponding set of three user sectors. Asis described below, the sets of traffic channels #1A, #2A and #3A may beselectively projected to each coverage area using horizontally-polarizedbeams, while the traffic channels #1B, #2B and #3B may be similarlyselectively projected using vertically-polarized beams. A PN long codegenerator (not shown) provides the long PN code used by the transmitters102A-102B, 104A-104B, and 106A-106B in modulating the informationsignals transmitted to each user sector. Again, the relative phases ofthe PN long codes supplied to the transmitters 102A-102B, 104A-104B, and106A-106B are offset by phase margins equivalent to a predeterminednumber of PN chips.

Within the transmitters 102A-102B, 104A-104B, and 106A-106B thePN-modulated information signals are used to bi-phase modulate aquadrature pair of sinusoids. The modulated sinusoids are then summed,bandpass filtered, shifted to an RF carrier frequency, and amplified.The outputs of each of the transmitters 102A-102B, 104A-104B, and106A-106B are respectively connected to six-way splitter networks112A-112B, 114A-114B, and 116A-116B. As is indicated by FIG. 4, thesplitter networks 112A-112B, 114A-114B, and 116A-116B are coupled to aswitch matrix 120.

The switch matrix 120 provides a switchable connection between theinformation signals transmitted over the paired sets of traffic channels(e.g. #1A and #1B) of each user sector and a set of six antenna drivers125A-125B through 130A-130B. Application of the output of each antennadriver 125A-130A to antennas 135-140 results in the projection ofhorizontally-polarized to beams coverage areas C1-C6, while applicationof the output of each antenna driver 125B-130B to antennas 135-140results in the projection of a vertically-polarized beam to eachcoverage area C1-C6. As is indicated by FIG. 4, the switch matrix 120 isconfigured such that the two sets of users associated with each usersector may be serviced within each of the coverage areas C1-C6.

Referring to FIG. 4, there is shown an illustrative representation ofthat portion of the switch matrix 120 operative to switchably connectthe six-way splitters 112A-112B to each of the antenna drivers 125A-125Bthrough 130A-130B. In particular, digitally-controlled attenuators 142and 144 are interposed between the outputs of the six-way splitters112A-112B and each of the antenna drivers 125A-125B through 130A-130B.In a preferred embodiment the switch matrix 120 includes two other setsof twelve digital attenuators (not shown), for switchably connecting thesplitters 114A-114B and 116A-116B to the antenna drivers 125A-125Bthrough 130A-130B.

Each pair of antenna drivers (e.g., drivers 125A-125B) is connected toone of six base station antennas 135-140, each antenna 135-140 beingoperative to project a horizontally-polarized and a vertically-polarizedbeam over one of the coverage areas C1-C6 (FIG. 1A). As noted above, ina preferred embodiment delays are introduced between the signalsprojected to any pair of adjacent coverage areas. Accordingly, alternatepairs of antenna drivers (e.g., drivers 125-125B, 127A-127B) aredisposed to provide delays slightly longer than a single PN chip period.In other respects the antenna drivers 125A-125B through 130A-130B aresubstantially similar to the antenna drivers 75-80.

FIGS. 5A and 5B respectively provide top and side views of a dual-moderesonant patch antenna capable of realizing the antennas 135-140. Thepatch element 160 shown in FIG. SA is one-half carrier wavelength ineach dimension and is suspended above a ground plane 162 (FIG. 5B) by apost 163. The patch element 160 is seen to be separated from the groundplane 162 by a separation distance S. In the preferred embodiment thedistance S is selected such that sufficient bandwidth is provided tospan both the transmit and receive frequency bands. Thevertically-polarized mode is created by resonating the patch element 160such that voltage maxima occur proximate upper and lower edges 170 and172 of the patch element 160, and such that a voltage null occurs in themiddle. Similarly, the horizontally-polarized mode is created byresonating the patch 160 such that voltage maxima arise at left andright edges 176 and 178 of the patch element 160. In a preferredembodiment the vertically-polarized mode is excited via a voltage probeapplied to the center of the upper 170 and lower 172 edges of the patchelement 160. In like manner, the horizontal mode is induced usingvoltage probes connected to the right and left edges 176 and 178.

III. Dynamic Sectorization within a Receive Network

Referring to FIG. 6, there is shown a block diagrammatic representationof a base station receiver network 200 configured to provide dynamicuser sectorization in accordance with the invention. The network 200 isseen to be generally complementary to the transmitter network 40 (FIG.2) in that a decorrelating delay is introduced between signals receivedfrom adjacent coverage areas. The receiver network 200 and thetransmitter network 40 may be simultaneously coupled to the antennas85-90 through a duplexer (not shown).

The signals received from the coverage areas C1-C6 through antennas85-90 are respectively provided to receive amplifiers 210-215. Thereceive amplifiers 210-215 each include a low-noise amplifier (LNA) 220having a passband centered about the frequency of the received RFcarrier. The amplifiers 210-215 are further seen to include delayelements 225A-225F capable of providing delays slightly longer than thechip period of the PN long code used to discriminate between usersectors. In a preferred embodiment alternate ones of the delay elements225A-225F (e.g., elements 225B, 225D, and 225F) are designed to providea delay slightly longer than a single PN chip period, while theremaining delay elements are omitted (zero delay). The delay elements225A-225F could be realized using one or more surface acoustic wave(SAW) filters. Alternatively, a coiled optical fiber of predeterminedlength could be used to create the desired delay.

The output of each delay element 225A-225F is provided to a 3-waysplitter 230 connected to a switch matrix 232. The switch matrix 232 issubstantially identical to the switch matrix 74, and hence provides aswitchable connection between each output of the 3-way splitters 230 andan input to one of three 6-way summation networks 240-242. The summationnetworks 240-242 are coupled to a corresponding set of three diversityreceivers 250-252 through amplifiers 254-256, each diversity receivercapable of being implemented in the manner described below withreference to FIG. 10. Each diversity receiver 250-252 frequencydownconverts, and digitizes the received signal into composite I and Qcomponents. The composite I and Q components then demodulated, combined,deinterleaved and decoded.

Each I and Q component may be comprised of data signals from a givensubscriber unit received by two or more of the antennas 85-90 associatedwith adjacent coverage areas C1-C6 of a given user sector. The receivedsignals associated with each coverage area, as selected by a searcherreceiver in combination with a controller, are each processed by adifferent one of multiple data receivers or demodulators, which are alsoreferred to as “fingers” (not shown). From the composite I and Qcomponents each finger extracts, by despreading, the I and Q componentsRI and RQ of the pilot and data signals associated with each coveragearea. A PN long code generator 260 provides the long PN code used by thereceivers 250-252 in demodulating the information signals received fromeach user sector. The relative phases of the PN long codes supplied tothe receivers 251-252 are offset by predetermined margins by phase delayelements 270 and 272, as illustrated. In the preferred embodiment, thephase delay elements 270 and 272 provide delays approximately equivalentin duration to 768 PN chips.

IV. Dynamic Sectorization within a CDMA System

Referring to FIG. 7, there is shown a block diagrammatic representationof a spread spectrum transmitter suitable for realizing the spreadspectrum transmitters 42, 44 and 46 (FIG. 2). The spread spectrumtransmitter of FIG. 7 is of the type described in U.S. Pat. No.5,103,459, issued 1992, entitled “System and Method for GeneratingSignal Waveforms in a CDMA Cellular Telephone System”, which is assignedto the assignee of the present invention, and which is hereinincorporated by reference. In the transmitter of FIG. 7, data bits 300consisting of, for example, voice converted to data by a vocoder, aresupplied to an encoder 302 where the bits are convolutionally encodedwith code symbol repetition in accordance with the input data rate. Whenthe data bit rate is less than the bit processing rate of the encoder302, code symbol repetition dictates that encoder 302 repeat the inputdata bits 300 in order to create a repetitive data stream at a bit ratewhich matches the operative rate of encoder 302. The encoded data isthen provided to interleaver 304 where it is interleaved. Theinterleaved symbol data is output from interleaver 304 at an exemplaryrate of 19.2 ksps to an input of exclusive-OR 306.

In the system of FIG. 7, the interleaved data symbols are scrambled toprovide greater security in transmissions over the channel. Scramblingof the voice channel signals may be accomplished by pseudonoise (PN)coding the interleaved data with a PN code specific to an intendedrecipient subscriber unit. These scrambling codes comprise the “inner”PN codes to which reference was made in the Background of the Invention.Such PN scrambling may be provided by the PN generator 308 using asuitable PN sequence or encryption scheme. The PN generator 308 willtypically include a long PN generator for producing a unique PN code ata fixed rate of 1.2288 MHz. This PN code is then passed through adecimator (not shown), with the resulting 19.2 MHz scrambling sequencebeing supplied to the other input of exclusive-OR 306 in accordance withsubscriber unit identification information provided thereto. The outputof exclusive-OR 306 is then provided to one input of exclusive-OR 310.

Again referring to FIG. 7, the other input of exclusive-OR gate 310 isconnected to a Walsh code generator 312. Walsh generator 312 generates asignal corresponding to the Walsh sequence assigned to the data channelover which information is being transmitted. The Walsh code provided bygenerator 312 is selected from a set of 64 Walsh codes of length 64. The64 orthogonal codes correspond to Walsh codes from a 64 by 64 Hadamardmatrix, wherein a Walsh code is a single row or column of the matrix.The scrambled symbol data and Walsh code are exclusive-OR'ed byexclusive-OR gate 310 with the result provided as an input to both ofthe exclusive-OR gates 314 and 316.

Exclusive-OR gate 314 also receives a PN_(I) signal, while the otherinput of exclusive-OR gate 316 receives a PN_(Q) signal. In CDMAapplications the PN long code generator 50 (FIG. 2) operates to provideboth PN_(I) and PN_(Q) sequences to the spread spectrum transmitters 42,44 and 46. The PN_(I) and PN_(Q) signals are pseudorandom (PN) signalscorresponding to a particular user sector covered by the CDMA system andrelate respectively to in-phase (I) and quadrature phase (Q)communication channels. The PN_(I) and PN_(Q) signals are respectivelyexclusive-OR'ed with the output of exclusive-OR gate 310 so as tofurther spread the user data prior to transmission. The resultingI-channel code spread sequence 322 and Q-channel code spread sequence326 are used to bi-phase modulate a quadrature pair of sinusoids. Eachquadrature pair of sinusoids is summed within transmitters 42, 44 and46, is shifted to an RF frequency, and is provided to one of theamplifiers 58, 60 and 62.

In the preferred embodiment, a pilot channel containing no datamodulation is transmitted together with the I-channel and Q-channelspread sequences S_(I) and S_(Q). The pilot channel may be characterizedas an unmodulated spread spectrum signal used for signal acquisition andtracking purposes. In systems incorporating a plurality of base stationtransmitters in adjacent cells, the set of communication channelsprovided by each will be identified by a unique pilot signal. However,rather than using a separate set of PN generators for the pilot signals,it is realized that a more efficient approach to generating a set ofpilot signals is to use shifts in the same basic sequence. Utilizingthis technique an intended receiver unit sequentially searches the wholepilot sequence and tunes to the offset or shift that produces thestrongest correlation.

Accordingly, the pilot sequence will preferably be long enough that manydifferent sequences can be generated by shifts in the basic sequence tosupport a large number of pilot signals in the system. In addition, theseparation or shifts must be great enough to ensure that there is nointerference in the pilot signals. Hence, in an exemplary embodiment thepilot sequence length is chosen to be 2¹⁵, which allows for 512 distinctpilot signals with offsets in a basic sequence of 64 chips.

Referring to FIG. 8, a pilot generation network 330 includes a Walshgenerator 340 for providing the Walsh “zero” W₀ sequence consisting ofall zeroes to exclusive-OR combiners 344 and 346. The Walsh sequence W₀is multiplied by the PN_(I) and PN_(Q) sequences using the exclusive-ORcombiners 344 and 346, respectively. Since the sequence W₀ includes onlyzeroes, the information content of the resultant sequences depends onlyupon the PN_(I) and PN_(Q) sequences. The sequences produced byexclusive-OR combiners 344 and 346 are provided as inputs to FiniteImpulse Response Filters (FIR) filters 350 and 352. The filteredsequences output from FIR filters 350 and 352, respectivelycorresponding to I-channel and Q-channel pilot sequences P_(I) andP_(Q), are supplied to the RF transmitter 382.

Referring to FIG. 9, there is shown an exemplary implementation of theRF transmitter 382. Transmitter 382 includes an I-channel summer 370 forsumming the PN_(I) spread data signals S_(Ii), i=1 to N, with theI-channel pilot P_(I). Similarly, a Q-channel summer 372 serves tocombine the PN_(Q) spread data signals S_(Qi), i=1 to N, with theQ-channel pilot P_(I). Digital to analog (D/A) converters 374 and 376are provided for converting the digital information from the I-channeland Q-channel summers 370 and 372, respectively, into analog form. Theanalog waveforms produced by D/A converters 374 and 376 are providedalong with local oscillator (LO) carrier frequency signals Cos(2ft) andSin(2ft), respectively, to mixers 388 and 390, where they are mixed andprovided to summer 392. The quadrature phase carrier signals Sin(2ft)and Cos(2ft) are provided from suitable frequency sources (not shown).These mixed IF signals are summed in summer 392 and provided to mixer394.

Mixer 394 mixes the summed signal with an RF frequency signal fromfrequency synthesizer 396 so as to provide frequency upconversion to theRF frequency band. The RF signal includes in-phase (I) and quadraturephase (Q) components, and is bandpass filtered by bandpass filter 398and output to one of the RF amplifiers 58, 60, 62 (FIG. 2). It should beunderstood that differing implementations of the RF transmitter 382 mayemploy a variety of signal summing, mixing, filtering and amplificationtechniques not described herein, but which are well known to those inthe art.

FIG. 10 is a block diagram of an exemplary diversity receiver associatedwith one of the subscriber units 12 (FIG. 1A), and hence is disposed toreceive the RF signals transmitted by one or more of the antennas 85-90of the base station 40 (FIG. 2). In FIG. 10, the RF signal transmittedby base station 40 is received by antenna 410 and provided to adiversity RAKE receiver which is comprised of analog receiver 412 anddigital receiver 414. The signal, as received by antenna 410 andprovided to analog receiver 412, may be comprised of multipathpropagations of the same pilot and data signals intended for individualor multiple subscriber receivers. Analog receiver 412, which isconfigured in the exemplary embodiment as a QPSK modem, frequencydownconverts, and digitizes the received signal into composite I and Qcomponents. The composite I and Q components are provided to digitalreceiver 414 for demodulation. The demodulated data is then provided todigital circuitry 416 for combining, deinterleaving and decoding.

Each I and Q component output from analog receiver 412 may be comprisedof corresponding data signals transmitted by two or more of the antennas85-90 associated with adjacent coverage areas C1-C6 of a given usersector. As discussed above, a phase offset is introduced between thedata signals provided to adjacent coverage areas in a particular usersector. In digital receiver 414 the received signals associated witheach coverage area, as selected by a searcher receiver 415 incombination with a controller 418, are each processed by a different oneof multiple data receivers or demodulators 420A-420C, which are alsoreferred to as “fingers”. Although only three data demodulating fingers(demodulators 420A-420C) are illustrated in FIG. 10, it should beunderstood that more or less fingers may be used. From the composite Iand Q components, each finger extracts, by despreading, the I and Qcomponents RI and RQ of the pilot and data signals associated with eachcoverage area.

In an exemplary implementation, each subscriber unit 12 is assigned oneof a set of a set of 64 orthogonal Walsh codes W_(i) of length 64. Thisallows a set of channels including a pilot channel, 63 I-channel, and 63Q-channels to be transmitted using a given pair of spreading sequencesPN_(I) and PN_(Q). The extracted pilot signal is used for time alignmentwithin a symbol combiner (not shown) within the subscriber unitreceiver. When the subscriber unit is positioned proximate the boundaryof adjacent coverage areas assigned to the same user sector, theestimates of the data transmitted to each coverage area are time-alignedand added together, thereby improving signal-to-noise-ratio.

V. Dynamic Sectorization Using In-Phase Beam Pattern

As was discussed above, in the preferred embodiment a delay isintroduced between the beams projected to adjacent antenna coverageareas so as to decorrelate the signals transmitted to each area. Thisapproach is designed to substantially eliminate destructive interferencebetween the beams provided to adjacent coverage areas, therebypreventing the formation of nulls and other beam pattern distortion. Adiversity receiver associated with a subscriber unit positioned near thecoverage area boundary is thus able to separately receive thedecorrelated signals, and to subsequently combine the separatelyreceived signals.

In an alternate embodiment of the invention the cellular base station isdesigned to effect dynamic user sectorization by providing a set offixed-beams projected in precise phase alignment. Referring to FIG. 11A,there is shown the azimuth pattern of a 40 degree fixed-beam assumed tobe projected by a first base station antenna, associated with one of thecoverage areas C1-C6 (FIG. 1A). If a second base station antenna,disposed to provide a second 40 degree fixed-beam to an adjacentcoverage area, is driven in phase with the first base station antennathe pattern shown in FIG. 11B is produced. It is thus apparent that thewidth of a user sector may be increased in proportion to the number ofbeams excited. Since the beams are generated in phase, the beamsconstructively interfere near coverage area boundaries and hence areeffectively coherently combined within the base station rather thanwithin the subscriber unit receiver.

Referring to FIG. 12, there is shown a block diagrammatic representationof a base station transmitter network 440 configured to provide dynamicuser sectorization by projecting a set of in-phase beams to each usersector. The network 440 is seen to be substantially similar to thenetwork of FIG. 2, where like reference numerals are used in identifyingsubstantially similar system components. Rather than including phasedelay elements 95A-95F, the antenna drivers 75-80 are seen to includephase equalizers 444A-444F adjusted such that the antennas 85-90 aredriven in phase. Adjustment of the equalizers 444A-444F may beperformed, for example, during base station installation by applying anidentical test signal to each driver 75-80.

More specifically, during a calibration procedure a set of test signalsof identical amplitude and phase are provided to the antenna drivers75-80. The outputs of adjacent pairs of antenna cables 445A-445F,respectively associated with the antennas 85-90, are then connected tothe dual input ports of a power combiner. The phase equalizer within theantenna driver coupled to one of the antenna cables is then adjusteduntil the output of the power combiner is maximized. This procedure isrepeated for each adjacent pair of antenna drivers, i.e., for thedrivers 75 and 76, the drivers 76 and 77, and so on.

An analogous procedure is used to calibrate the receive network 200(FIG. 6). In particular, a set of test signals of identical amplitudeand phase are injected at the ports of the antenna cables 224A-224Fnominally coupled to the antennas 85-90. A power combiner having sixinput ports and a single output port is then connected to the splitters230 of an adjacent pair of the receive amplifiers 210-215. A phaseequalizer (not shown) within one of the receive amplifiers connected tothe power combiner is then adjusted until output power from the combineris maximized. This process is then repeated for each adjacent pair ofreceive amplifiers 210-215.

FIG. 13 depicts an alternate base station configuration 450 forproviding dynamic user sectorization by projecting a set of in-phasebeams. As is indicated by FIG. 13, phase alignment is maintained betweenadjacent beams by locating the switch matrix and antenna driversproximate the antennas 85-90. That is, in the configuration of FIG. 13the switch matrix 74 and antenna drivers 85-90 follow, rather thanprecede, the transmission cables 452-454 within the base station antennatower 458. The direct coupling of the drivers 75-80 to the antennas85-90 advantageously prevents phase differences due to cable lengthvariations, and the like from being introduced between the beamstransmitted to adjacent coverage areas.

VI. Antenna Subsystem

In both the decorrelated phase and controlled phase embodiments of theinvention (see, e.g., FIGS. 2 and 12), the size of a given user sectoris varied by using a combination of one or more beams to provide theinformation signal for the sector. Each such beam may be created usingany one of a number of conventional techniques. For example, a set ofdistinct fixed-beam antennas could be used to project a set of beams ofpredetermined angle. In this approach the antennas are mounted andaligned such that each beam encompasses a predetermined coverage area.In an exemplary embodiment a set of six antennas are used to provide a60 degree beam to each of six coverage areas (see, e.g., FIG. 1A).

Alternately, a phased array antenna may be used to simultaneously formmore than a single beam. For example, FIG. 14 shows a triangulararrangement of first, second and third phased array antenna panels 480,482 and 484, which collectively operate to provide a set of nine antennabeams to coverage areas C1-C9. In particular, antenna panel 480 projectsthree 40-degree fixed beams to coverage areas C1-C3, while antennapanels 484 and 482 project 40-degree fixed-beams to coverage areasC4-C6, and C7-C9, respectively.

As is indicated by FIG. 15, in a preferred implementation the face ofeach antenna panel includes a 4×4 array of patch elements, the elementswithin each column being respectively identified by the referencenumerals 486-489. Assuming an RF carrier frequency of 850 MHz, eachpatch element may be fabricated from a square section ofdielectrically-loaded patch material of area 4 in². This results in eachsquare antenna panel 482-484 (FIG. 14) being of an area of approximately4 sq. ft.

Referring to FIG. 16, there is shown a phased array antenna andbeam-forming network 490 disposed to provide three beams from a singleantenna face. A switch matrix (not shown) provides the informationsignals corresponding to user sectors #1, #2 and #3 via input signallines 494A-494C. The beam-forming network 490 includes 4-way splitters495A-495C, respectively connected to signal lines 494A-494C. The fouroutputs from each splitter 495A-495C are connected via phase delayelements 496 to one of four summation nodes 498-501. The compositesignals from summation nodes 498-501 are respectively provided to poweramplifiers 504-507. As is indicated by FIG. 16, each column of arrayelements 486-489 is driven by one of the amplifiers 504-507. Inalternate implementations, a separate power amplifier is utilized todrive each array element 486-489.

In an exemplary embodiment, the delay elements 496 are adjusted suchthat each of three beams are projected at a 40-degree angle to one ofthree adjacent coverage areas. The three beams projected by a singleantenna panel would then span an arc of 120 degrees. Three such panelscould be mounted to provide a set of nine beams encompassing an arc of360 degrees.

The previous description of the preferred embodiments is provided toenable any person skilled in the art to make or use the presentinvention. The various modifications to these embodiments will bereadily apparent to those skilled in the art, and the generic principlesdefined herein may be applied to other embodiments without the use ofinventive faculty. Thus, the present invention is not intended to belimited to the embodiments shown herein but is to be accorded the widestscope consistent with the principles and novel features disclosedherein. For example, in addition to addressing the need for flexibletraffic channel allocation as a consequence of short-term changes inuser demand, the method and apparatus of the invention may be employedto accommodate long-term changes in user demand. Such long-termvariation in demand could accompany, for example, shifts in populationdistribution and building patterns within a given geographic area.

What is claimed is:
 1. A system for conveying information to at leastone user in a first user sector of a spread spectrum communicationsystem, said system comprising: a first PN signal generator forgenerating a first PN signal of a first predetermined PN code; a firstsignal combiner, coupled to said first PN signal generator, whichcombines said first PN signal and a first information signal andgenerates a first modulated information signal; a delay network forgenerating a second modulation signal by delaying said first modulationsignal by a predetermined time period; and an antenna for varyingboundaries of a first user sector by transmitting said first modulationsignal to a first coverage area during a first time period, and bytransmitting said first and second modulation signals to said firstcoverage area and to a second coverage area during a second time period.2. In a cellular subscriber communication system in which users withinat least one cell communicate information signals between one anothervia at least one cell-site using spread spectrum communication signalswherein each of said at least one cell-site includes a cell-sitetransmitter network, said transmitter network comprising: a delaycircuit for receiving a first set of spread spectrum information signalsand generating a second sets of spread spectrum information signals fromsaid first set of spread spectrum information signals by delaying by apredetermined time period each of said spread spectrum informationsignals included within said first set of spread spectrum informationsignals; a first antenna, configured to receive said first set of spreadspectrum information signals and transmit said first set of spreadspectrum information signals to a first coverage area within a cell; anda second antenna, coupled to the delay circuit, configured to transmitsaid second set of spread spectrum information signals to a secondcoverage area within said cell, wherein said first user sector includessaid first coverage area when said second set of spread spectruminformation signals is not transmitted and includes said first andsecond coverage areas when said first and second sets of spread spectruminformation signals are transmitted.
 3. A method of conveyinginformation to at least one user in a spread spectrum communicationsystem, said method comprising the steps of: generating a first PNsignal of a first predetermined PN code; combining said first PN signaland a first information signal, and generating a first modulatedinformation signal; selectively generating a first modulation signalfrom said first modulated information signal; selectively generating asecond modulation signal from said first modulated information signal,said second modulation signal delayed from said first modulation signalby a predetermined time period; and transmitting said first and secondmodulation signals respectively to first and second coverage areasdefining boundaries of a first user sector; and whereby boundaries ofsaid first user sector are adjusted by transmitting only one of saidfirst and second modulation signals to a respective coverage area.